CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:NMattermost versions 10.11.x <= 10.11.18, 11.6.x <= 11.6.3, 11.5.x <= 11.5.6 fail to validate attachment URLs against internal or private IP ranges in the Mattermost Agents plugin MCP server which allows an attacker with access to the MCP server in stdio mode to perform server-side request forgery (SSRF) and exfiltrate data from internal network services via supplying internal URLs as file attachments in post creation requests.. Mattermost Advisory ID: MMSA-2026-00635
Multiple vulnerabilities have been discovered in Mattermost Server, allowing attackers to compromise data confidentiality and bypass security policies. These vulnerabilities, detailed in Mattermost security bulletins, re…